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The Supernova Legacy The Supernova Legacy Survey (SNLS): Survey (SNLS):
New Results on Cosmology New Results on Cosmology and the Nature of Type Ia and the Nature of Type Ia
SupernovaeSupernovae
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Toronto Group
Ray Carlberg, Mark Sullivan, Andy Howell, Kathy Perrett,
Alex Conley
French Group
Reynald Pain, Pierre Astier, Julien Guy, Nicolas Regnault,
Jim Rich, Stephane Basa, Dominique Fouchez
UK
Gemini PI: Isobel Hook + Justin Bronder, Richard McMahon, Nic Walton
Victoria Group
Chris Pritchet, (Don Neill), Dave Balam, Eric Hsiao, Melissa
Graham
USA
LBL: Saul Perlmutter CIT: Richard Ellis
Plus: Many students and associate members throughout the world
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Special Mention …
Andy Howell – PDF U.Toronto
Melissa Graham U Victoria
Alex Conley – PDF U Toronto
Eric Hsiao U Victoria
Mark Sullivan – PDF U Toronto
Kathy Perrett – PDF U Toronto, Ms. Data
Dave Balam, RA, U Victoria
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Historical Background Supernova Cosmology SNLS Overview SNLS Results Other SN Science Conclusions/Future
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Golden Moments in Cosmology Golden Moments in Cosmology
μνμν πT
c
GG
4
8−= μνμνμν π
gTc
GG Λ−−=
4
8
repulsive forcerepulsive force, vacuum energy, ρρ=const =const
“Much later, when I was discussing cosmological problems with Einstein, he remarked that the introduction of the cosmological term was the biggest blunder of his life.” – G. Gamow, “My World Line” (1970)
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Hubble Diagram (ℓ vs z)
faintbrightnearby
distant
V [
km/s
]
Assumptions: Inverse square law ℓ =L/4πd² Euclidean space Standard candle
(what Hubble actually did to demonstrate the expansion of the Universe)
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Hubble Diagram and Cosmology
log d or log z
log
appa
rent
brig
htne
ss
Ω=1Ω<1
Ω>1
Curvature of space causes deviations from linear Hubble diagram.
Ω<1 means expansion forever.
Standard candle!
High ρ
Low ρ
z = v/c = Δλ/λ
1+z = Ro/R
flatflat
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Hubble 1953Hubble 1953
Cosmology – A Search for 2 Numbers?Cosmology – A Search for 2 Numbers?
Ho– rate of expansion (v=Hod)Ωo – deceleration - matter density
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Gunn and Oke 1975
“… although the heterogeneity of the sample makes conclusions about cosmology slightly suspect.”
-2 < Ω <0
+2 < Ω < +4
Kristian, Sandage and Westphal 1978
>400 nights >400 nights of Palomar of Palomar 200” time!200” time!
evolution (mass and age)
evolution (mass and age)
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Historical Background Supernova Cosmology SNLS Overview SNLS Results Other SN Science Conclusions/Future
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SNe Ia vs SNe II – a PrimerSNe Ia vs SNe II – a Primer
SN IaSN Ia SN IISN IIbrightness 1010 Lsun ~109 Lsun
progenitor 1 or 2 white dwarfs (M>1.4Msun)
massive star
mechanism mass transfer or merger; thermonuclear disruption
core collapse
progenitor age ~1010 yr ~107 yr
evolution with z Little? (1+z) 2-4 :
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Making a standard candle Phillips 1993
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Making a standard candle
csMMOBB βα −−+= )1(
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Supernovae as Cosmological Probes
Max brightness makes an excellent standard candle - ±6% distance errors
Bright - can be seen to cosmological distances
Standard candle has a physical basis• SNeIa are “well-understood” - thermonuclear
disruptions of C+O white dwarfs - std physics
“The supernova distance-redshift relation comes from the FRW metric. That’s it. Issues of DE sound speed, anisotropic stress, matter growth, etc, do not affect this probe.” (Linder 2006)
Systematics – possibly, but ample opportunity to study with potentially hundreds of objects
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Supernovae and Dark EnergySupernovae and Dark Energy
Not:i/s abs (hi z)evolution selection effects
Riess et al. 1998Riess et al. 1998Perlmutter et al. 1999Perlmutter et al. 1999
Cosmological constant Λ
Universe is accel-erating. Λ exists!
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Dark Energy - a Strange Brew …
Expansion is accelerating Vacuum energyVacuum energy, , ρ ≈ const
• Einstein was right! ΩΩtottot=Ω=ΩMM+Ω+ΩDEDE=1=1
ρΛ ≈ 10-8 eV cm-3 ≈ 10-120 x “theoretical value” ρΛ ≈ ρM – why??
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““On a good day I can think of 3 or 4 On a good day I can think of 3 or 4 plausible candidates for dark plausible candidates for dark matter. The same cannot be said matter. The same cannot be said for dark energy.”for dark energy.” - Rocky Kolb, Tucson, Mar 2004
“Our theoretical understanding is so limited right now …” - Rocky Kolb, Tucson, Mar 2004
“… DE is not understood sufficiently to answer the basic questions …” - Rocky Kolb, Tucson, Mar 2004
Rocky Horror Show – Tucson 2004
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What is What is the Dark the Dark Energy?Energy?
What is it ??What is it ??
Copeland et al astro-ph/ 0603057
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What is the DE?What is the DE?
Cosmological Constant Λ Pure vacuum energy
Some other new physical component
e.g. scalar field models, quintessence, Chaplygin gas models
A new physical law e.g. modifications to GR
What is it ??What is it ??
“Raffiniert is der Herrgott, aber boshaft ist er nicht.” (Einstein)
(Einstein’s translation: “God is slick, but he ain’t mean.”)
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Equation of State Parameter “w”Equation of State Parameter “w”
P = wρ(a) ~ a-3(1+w)
w = 1/3 radiation w = 0 matterw > -1 “quintessence”w = -1 w = -1 ΛΛ
w is a measurable. most sensitivity at z<1. w,dw/dz constrain DE.
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Background Supernova Cosmology SNLS Overview SNLS Other SN Science Conclusions
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MegaCam at CFHT
Built by CEA 1 deg x 1 deg field 40 x (2048 x 4612) chips • ~ 400Megapixels good blue response
““Size matters Size matters …”…” Anon.
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CFHT Legacy CFHT Legacy SurveySurvey
SNLS - Deep SNLS - Deep (“SNe + galaxy evolution”)(“SNe + galaxy evolution”) 4 deg², long time sequenced exposures 202 nights
Wide (“weak lensing”)Wide (“weak lensing”) 172 deg² in 3 patches
Very Wide Very Wide (“KBO”)(“KBO”) 1300 deg², +-2 deg from ecliptic, short exposures
470 nights (dark-grey) 470 nights (dark-grey) over 5 years (2003-2008)over 5 years (2003-2008)
Hoekstra et al 2006 astro-ph/0511089
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202 nights over 5 years 202 nights over 5 years (part of CFHTLS) four 1 degfour 1 deg² ² fieldsfields queue scheduled obs, queue scheduled obs, 3-4 day temporal sampling3-4 day temporal sampling ggrriizz filters (450-950nm)filters (450-950nm) spectroscopic followup (VLT, Gemini, Keck, Magellan)spectroscopic followup (VLT, Gemini, Keck, Magellan) 2 independent search, photometry, cosmology pipelines >500 SNeIa>500 SNeIa over 5 yrs with spectroscopic type over 5 yrs with spectroscopic type
SNLS in a nutshellSNLS in a nutshell
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SNLS SNLS – multiband– multiband SNLS provides the definitive high-z SN
dataset for the next 5+ years. Multi-band g’r’i’z’ photometry is the key: Wide z range 0.2-0.9 Better control over systematics: SN colour
evolution Better control over dust: Extinction corrections
using rest-frame U-B & B-V Better control over k-corrections: wider
wavelength coverage Better estimates of rest-frame B-band
luminosities
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•2 pipelines•Data stays in Hawaii, remote real-time access•90% agreement i’~24•Short turnaround (6 hr to spec candidates)
Two Search Pipelines (Ca, Fr)
K. Perrett
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>1700 since Aug 2003!>1700 since Aug 2003!
Detections
04D2ca 04D2ca z=0.83 Mar 10z=0.83 Mar 10
ACSACS
~10-4 of total Megacam area
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D2 Cosmos ACS
imaging ~7 x 7
arcsec +-
Note diversity
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Rolling Search
griz (redshift 0.2-0.9) 2-3 day sampling restframe 12 month observing
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Typical light-curves
z=0.36
z=0.91
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Spectroscopy
CFHT Gemini-N
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Follow-up Spectroscopy Follow-up Spectroscopy (types and redshifts)(types and redshifts)
Keck (~8 nights/yr) Ellis / Perlmutter
VLT (120 hr/yr)France/UK: FORS1/2 to get types & redshifts for SNe (0.3 < z < 0.8)
Gemini N & S (120 hr/yr)Canada/UK/US GMOS to get types/redshifts for SNe (0.6 < z < 0.9)
More 8-10m time than CFHT timeMore 8-10m time than CFHT time
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N(z) to 2006 (N ~ 300)
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SNLS: Current and projected numbers
Currently >350 spec confirmed
SNe Ia
400-500 spec confirmed SNeIa by survey end
(>1000 total)
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Historical Background Supernova Cosmology SNLS Overview SNLS Results Other SN Science Conclusions/Future
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Distance estimator: stretch and colour
Distance estimator used:
s, c terms dominate; no need for other terms
s – “stretch” corrects s – “stretch” corrects for light-curve shape for light-curve shape
via via αα
““c” – B-V colour corrects c” – B-V colour corrects for extinction (and for extinction (and
intrinsic variation) via intrinsic variation) via ββ
csMm BBB ×−−+−= βαμ )1(
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First YearFirst Year Cosmology Cosmology (Astier et al. 2006)(Astier et al. 2006)
First year results (72 SNe Ia) consistent with
an accelerating Universe: ΩM=0.263 in
a flat universe
Intrinsic disp.: 0.13 ± 0.02Low-z: 0.15 ±0.02
SNLS: 0.12 ± 0.02z’ errors – now observing 3x longer
csMmBB βαμ +−+−= )1(
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w = -1.02 w = -1.02 ± 0.09± 0.09
N=71, one year, SNLS+low z only w to ~±0.05 by 2008 (why not +-0.03?)
Astier et al 2006
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WMAP3 constraints
Spergel et al 2007
073.0072.0967.0w +
−−=
Assumptions: flat universe, perturbations in dark energy
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2007 – prelim! ~230 out of 270
SNeIa, to Aug 2006
Fit - w=-1
SNLS 3rd year analysis
Preliminary
Cuts:Stretch 0.75<s<1.25ColourLight curve coverage
Intrinsic scatter: SNLS ±0.09 Low z ±0.13
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Residuals vs. SFR
Passive galaxies
Green=moderate star formation
Blue=active star formation
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Addressing systematics
The control of systematics will define how accurately w and especially dw/dz will be determined
Large sample size of SNLS will allow subsample tests to investigate role of systematics
Largest systematics currently are:
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Systematics …
ZP uncertainty ±0.04 in w
Improve mosaic uniformity to better than 1% (done)
Tie calibration to CALSPEC standards (precise flux standards)
Tie low and high z SNe together on uniform photometric system (SDSS-II)
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Systematics …
k-corrections (Hsiao et al 2007)
Based on 800 individual spectra (Suspect, etc) Ellis et al 2007 UV
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Systematics …
Malmquist Bias ±0.025 in w (Perrett 2007)
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Systematics …
Redshift dependent population changes• Sullivan et al …
Redshift evolution in SN properties• Conley et al, Bronder et al …
Selection by SN photo-z?Sullivan et al 2005
•1000 candidates – how to prioritize for followup? Defines success of survey.•Photometric pre-selection. Fits early-time SN light-curves, returns probability of the candidate being a SN Ia.
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Historical Background Supernova Cosmology SNLS Overview SNLS Results Other SN Science Conclusions/Future
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Other SN science
Howell et al 2006 (Nature, Sep 2006) – SN 03D3bb – a super-Chandra mass SN Ia – evidence for double degenerate merger?
Sullivan et al 2006 – SNIa rate depends strongly on host SFR
Pritchet et al 2007 - Interpretation of SNIa rate vs. SFR diagram, nature of SNIa Progenitors
Neill et al 2006 – best determination of absolute SN Ia rate
Conley et al 2006 – SN light curve shapes are identical at low and high z
Nugent et al 2006 – first ever SN II Hubble diagram
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SN Ia Progenitors
Single Degenerate - white dwarf + evolving secondary (M=1.4 Msun at explosion)
Double Degenerate - 2 white dwarfs (M >= 1.4 Msun at explosion)
Key point: white dwarf max mass = 1.4 Msun (Chandrasekhar mass)
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SNLS-03D3bb (Howell et al. 2006)
z=0.24, star-forming host
Most luminous SNIa ever discovered (MV=-20.0, 10 billion Lsun)
Lies off the stretch-L relation - too bright for its stretch s=1.13 by 4.4 sigma
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03D3bb
Requires 1.3 Msun of 56Ni to power light curve, 2Msun total mass
“normal” SNIa – 0.6 Msun of 56Ni 03D3bb is 2.2x brighter,
therefore has 2.2x Ni mass Detailed calculation using Arnett
models agrees well
Mass > Chandra mass of 1.4 Msun!
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03D3bb
Low velocity of ejecta (8000 km/s)
Also implies super-Chandra mass
Conclusion: either (i) a rapidly rotating WD, or (ii) WD-WD merger
Implications for cosmology (this object was not used in Astier et al 2006)
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Other SN science
Howell et al 2006 (Nature, Sep 2006) – SN 03D3bb – a super-Chandra mass SN Ia – evidence for double degenerate merger?
Sullivan et al 2006 – SNIa rate depends strongly on host SFR
Pritchet et al 2007 - Interpretation of SNIa rate vs. SFR diagram, nature of SNIa Progenitors
Neill et al 2006 – best determination of absolute SN Ia rate
Conley et al 2006 – SN light curve shapes are identical at low and high z
Nugent et al 2006 – first ever SN II Hubble diagram
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SNeIa in Star-Forming Galaxies
Mannucci et al 2006
SFRBMA ⋅+⋅=rateSNScannapieco and Bildsten 2006
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m = 1.10+-0.12, n = 0.84+-0.09A=5.1E-14 SNe/yr/MsunB=4.1E-4 SNe/yr/(Msun/yr)B needed at 99.99% confidence
€
SN rate = A ⋅Mm + B ⋅SFR n
cf. Scannapieco and Bildsten 2005 (m=1, n=1)
Bivariate fits give m,n close to 1
Sullivan et al 2006
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SN Ia rate depends on SFR
SFR½
€
cf . SNR /M = A + B(SFR /M)
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Meaning of A٠M + B٠SFR
Does this imply two paths to SNeIa? … … or is there a simple unifying picture that can be
used to understand the A+B prescription for the SNIa rate?
Why do the A and B values have the values that are observed?
Continuum of delay times – more natural? Why ~√SFR dependence rather than ~SFR?
)/(/ MSFRBAMSNR +=
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Single degenerate scenario Delay time depends on evolutionary timescale
of secondary - T(evol) ≈ T(ms) Simple SFR(t) ~ t-η to allow for range of ages
Toy Model
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Models vs Observations
Locus of WD formation rates independent of SFR(t)
1% of WD’s become SNeIa
1% agrees with models (roughly)
1% agrees with MW (roughly)
Disagrees with clusters (10-20%)
Note that 1% eff is constant from active to passive galaxies!
age
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Meaning
Single component model – not A+B
Continuous distribution of delay times
Rate in active and passive galaxies both explained
Only physics is evol timescales
Single free parameter normalization - fSNIa
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Efficiency vs mass
1 Msun main sequence stars find it very difficult to get to the Chandra mass and make a Type Ia SN
• Close binaries M1 < 2Msun make a He WD, not a C+O WD
• Mass arguments: 1 Msun on the m.s. makes a 0.5 Msun WD, hard to imagine 2 x 1 Msun making a 1.4 Msun WD
• Most of companions to 1 Msun stars haven’t evolved yet
• binary frequency lower for low mass objects (?)
Therefore fraction of WD’s that make SNeIa should be much lower at low masses (>10x).
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Effects of efficiency
Normalized at high mass (short timescale) end Assume efficiency drops by 10x from M=3 to 1 Msun (conservative)
Single degenerate model cannot explain all SNeIa. Some other mechanism must be involved for at least some SNeIa.
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Cosmic SFR(z)
Hopkins 2006
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SNR predictions from SFR(z)
Dot-dash=A+B
normalization arbitrary
Per Mpc^3
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Poznanski 2007
Dahlen 2004Neill 2006
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Historical Background Supernova Cosmology SNLS Overview SNLS Results Other SN Science Conclusions/Future
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ConclusionsConclusions
w = -1 (preliminary) from 3rd year data (N=230). Dark energy resembles pure cosmological constant (vacuum
energy). Most accurate estimate of w yet
SNIa rate depends on SFR progenitors found in young and old stellar populations Natural explanation from evolutionary timescales 1% of white dwarfs become SNeIa SNeIa not only from single degenerate progenitors
~400-500 SNeIa with spectroscopy by 2008, >1000 total
SNLS-2? ~60 deg^2, z<0.7, N=3000:
Stay tuned!
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More SNLS information http://legacy.astro.utoronto.ca/ - database (Perrett) www.cfht.hawaii.SNLS – people, papers, …
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Special Mention …
Andy Howell – PDF U.Toronto
Melissa Graham U Victoria
Alex Conley – PDF U Toronto
Eric Hsiao U Victoria
Mark Sullivan – PDF U Toronto
Kathy Perrett – PDF U Toronto, Ms. Data
Dave Balam, RA, U Victoria